Well, I'll be darned! I went back today and looked at the brick walls again, late in the day (4:30PM). It was sunny and warmer today, with highs near 27 degrees. The patterns on those walls was different. There was still the same type of pattern, but the warmer portion extended much lower on the wall. I then scanned the brick using my Delmhorst Tech-Check moisture meter. I was getting readings of zero on most of the walls, down to the areas that showed cooler. I was getting readings of 150 to around 230 (on a relative scale of 0-300) on those cooler areas down low. We have not had any precipitation except some flurries. It had not been warm enough to melt snow on the roof. I had thought of moisture, but didn't see how it could be a factor. (Actually, there was more "drip" from the roof today than when those images were taken.)
I also checked the south-facing walls (the sun was just starting to set) and found them to be around 4-5 degrees warmer, with no colder area at the bottom. Moisture scanning gave me readings in the vicinity of 150-230 (relative) over all of the south facing brick. So it appears that John was right. I was seeing moisture.
Brad Cook
Building Performance Services LLC
Warren, Vermont
Level I Thermographer
Home Performance Contractor